eg. A solution of Lead Nitrate reacts with a solution of Aluminium Chloride. Solution means in water = (aq)
Step 1. Determine the symbol and charge of each ion (the numerals in () represent the ion’s charge) but write the cation (+ ions) before the non-metal anion(s) (- ions) except for substances with acetate.
Step 2. To write a chemical formula, write ONE of each ion & balance the ion charges so the total is 0 by writing the required coefficient to the bottom right of the ion. For multiples of an atom group, use ( ). eg. Al3+Cl-, Charge number of Al is a 3 and the charge number of Cl is a 1 so Al1Cl3 but write it as AlCl3 eg. Pb2+NO3- . Charge number on Pb is a 2, and NO3 is only a 1 so Pb1(NO3)2 but write it as Pb(NO3)2.
Step 3. To balance one side (products or reactants), the total charge number must be same for both sides of the --> so find a common multiple and write the required coefficient in front of each chemical. eg. Charge number of Pb(NO3)2 is 2 and the charge number of AlCl3 is 3. Both 2 and 3 go into 6 so use 3 Pb(NO3)2 and 2 AlCl3. eg. 3 Pb(NO3)2 + 2 AlCl3 --->
Step 4. When reacting the cations and anions swap partners so write each ion in the products. eg. 3 Pb2+(NO3-)2 + 2 Al3+(Cl-)3 ---> Pb2+Cl- + Al3+(NO3-) If H2CO3 is produced, change it to H2O(l) + CO2(g).
Step 5. Repeat STEPS’ 2 and 3 to balance the charges of the products and write the final equation including states. eg. 3 Pb(NO3)2(aq) + 2 AlCl3(aq) ---> 3 PbCl2(s) + 2 Al(NO3)3(aq) Regard H2O as H+ and OH- if hydroxide ions are present or as 2 H+ and O2- if oxide ions are present.
QUESTIONS:
1. Determine the charges of each ion in each of the following compounds:- a). LiCl. b). Na2CO3. c). AlCl3. d). Na3PO4. e). K2SO4. . Li = _, Cl = _ Na = _, CO3 = _ Al = _, Cl = _ Na = _, PO4 = _ K = _, SO4 = _
2. Balance the following equations (the states have been omitted deliberately): a). LiOH + K2CO3 ---> Li2CO3 + KOH b). H2SO4 + NaCl ---> Na2SO4 + HCl c). LiOH + _ H2SO4 ---> Li2SO4 + H2O d). AgNO3 + FeCl2 ---> Fe(NO3)2 + AgCl e). Cu(NO3)2 + KOH ---> Cu(OH)2 + KNO3
3. Write balanced chemical equations for the following reactions showing the possible products: a). A solution of silver nitrate reacts with a solution of potassium chloride. b). A solution of iron(II) chloride reacts with a solution of lithium hydroxide. c). A solution of potassium hydroxide reacts with a solution of nitric acid (HNO3). d). A solution of aluminium nitrate reacts with a solution of copper sulfate. e). A solution of strontium chloride reacts with a solution of lead(II) bicarbonate (hydrogen carbonate). f). A solution of lead nitrate reacts with a solution of copper chloride.
Valency tables
CATIONS
View an animation of balancing to further understand this process
Here is a worked example
eg. A solution of Lead Nitrate reacts with a solution of Aluminium Chloride. Solution means in water = (aq)Step 1. Determine the symbol and charge of each ion (the numerals in () represent the ion’s charge) but write the cation (+ ions) before the non-metal anion(s) (- ions) except for substances with acetate.
Step 2. To write a chemical formula, write ONE of each ion & balance the ion charges so the total is 0 by writing the required coefficient to the bottom right of the ion. For multiples of an atom group, use ( ).
eg. Al3+Cl-, Charge number of Al is a 3 and the charge number of Cl is a 1 so Al1Cl3 but write it as AlCl3
eg. Pb2+NO3- . Charge number on Pb is a 2, and NO3 is only a 1 so Pb1(NO3)2 but write it as Pb(NO3)2.
Step 3. To balance one side (products or reactants), the total charge number must be same for both sides of the --> so find a common multiple and write the required coefficient in front of each chemical.
eg. Charge number of Pb(NO3)2 is 2 and the charge number of AlCl3 is 3. Both 2 and 3 go into 6 so use 3 Pb(NO3)2 and 2 AlCl3. eg. 3 Pb(NO3)2 + 2 AlCl3 --->
Step 4. When reacting the cations and anions swap partners so write each ion in the products.
eg. 3 Pb2+(NO3-)2 + 2 Al3+(Cl-)3 ---> Pb2+Cl- + Al3+(NO3-) If H2CO3 is produced, change it to H2O(l) + CO2(g).
Step 5. Repeat STEPS’ 2 and 3 to balance the charges of the products and write the final equation including states. eg. 3 Pb(NO3)2(aq) + 2 AlCl3(aq) ---> 3 PbCl2(s) + 2 Al(NO3)3(aq)
Regard H2O as H+ and OH- if hydroxide ions are present or as 2 H+ and O2- if oxide ions are present.
QUESTIONS:
1. Determine the charges of each ion in each of the following compounds:-a). LiCl. b). Na2CO3. c). AlCl3. d). Na3PO4. e). K2SO4. .
Li = _, Cl = _ Na = _, CO3 = _ Al = _, Cl = _ Na = _, PO4 = _ K = _, SO4 = _
2. Balance the following equations (the states have been omitted deliberately):
a). LiOH + K2CO3 ---> Li2CO3 + KOH b). H2SO4 + NaCl ---> Na2SO4 + HCl
c). LiOH + _ H2SO4 ---> Li2SO4 + H2O d). AgNO3 + FeCl2 ---> Fe(NO3)2 + AgCl
e). Cu(NO3)2 + KOH ---> Cu(OH)2 + KNO3
3. Write balanced chemical equations for the following reactions showing the possible products:
a). A solution of silver nitrate reacts with a solution of potassium chloride.
b). A solution of iron(II) chloride reacts with a solution of lithium hydroxide.
c). A solution of potassium hydroxide reacts with a solution of nitric acid (HNO3).
d). A solution of aluminium nitrate reacts with a solution of copper sulfate.
e). A solution of strontium chloride reacts with a solution of lead(II) bicarbonate (hydrogen carbonate).
f). A solution of lead nitrate reacts with a solution of copper chloride.
ANSWERS:
1. a). Li+(aq) , Cl-(aq). b). 2 Na+(aq) , CO32-(aq). c). Al3+(aq) , 3 Cl-(aq). d). 3 Na+(aq) , PO43-(aq). e). 2 K+(aq) , SO42-(aq).
2. a). 2 LiOH + K2CO3 --> Li2CO3 + 2 KOH. b). H2SO4 + 2 NaCl --> Na2SO4 + 2 HCll. c). 2 LiOH + H2SO4 --> Li2SO4 + 2 H2O,
d). 2 AgNO3 + FeCl2 ---> Fe(NO3)2 + 2 AgCl. e). Cu(NO3)2 + 2 KOH --> Cu(OH)2 + 2 KNO3..
3. a). AgNO3(aq) + KCl(aq) --> AgCl(s) + KNO3(aq). b). FeCl2(aq) + 2 LiOH(aq) --> Fe(OH)2(s) + 2 LiCl(aq).
c). KOH(aq) + HNO3(aq) --> KNO3(aq) + H2O(l). d). 2 Al(NO3)3(aq) + 3 CuSO4(aq) --> 3 Cu(NO3)2(aq) + Al2(SO4)3(aq).
e). SrCl2(aq) + Pb(HCO3)2(aq) --> Sr(HCO3)2(aq) + PbCl2(s). f). Pb(NO3)2(aq) + CuCl2(aq) --> PbCl2(s) + Cu(NO3)2(aq).